Risk factors for the 'jumper's knee'.

Risk factors for patellar tendinopathy: a systematic review of the literature. 
van der Worp,H., van Ark, M., Roerink, S., Pepping, G., van den Akker-Scheek, I. and Zwerver, J. British Journal of Sports Medicine, 2011; 45: 446 – 452. 
http://www.ncbi.nlm.nih.gov/pubmed/21367808

Patellar tendinopathy, so called “jumper’s knee”, is a common complain among jumping athletes as well as in those participating in endurance events. Identifying risk factors for particular condition seems crucial for developing preventive and rehabilitation interventions. Nevertheless, there seems to be no consensus in these areas in regards to the jumper’s knee. Therefore, authors decided to put together this systematic review to investigate risk factors for patellar tendinopathy.

The 11 included studies consisted of six cross-sectional, three case–control and one prospective cohort study. There was some evidence that increased weight, higher body mass index (BMI), higher waist-to-hip ratio, leg-length difference and lower arch height of the foot are risk factors for PT. Decreased quadriceps and hamstring flexibility, decreased quadriceps strength and better vertical jump performance were factors for which there was some evidence. No strong or moderate evidence could be obtained for any of the investigated factors.
Authors provide possible explanation for association between patellar tendinopathy and identified risk factors. The apparent association of weight and BMI with PT can be explained by a higher body mass theoretically leading to a higher loading of the patellar tendon, which increases changes of overload.
The possible association between leg-length difference and PT may be caused by the fact that the longer leg is the preferred take-off leg in jumping more often, which place higher load in this leg.
Quadriceps and hamstring flexibility may be associated with PT because decreased flexibility increases tendon strain during joint movements, and may therefore lead to tendon overload.
Lower quadriceps strength may be caused by atrophy as a result of inactivity brought about by PT, yet it may also be the cause of PT.
Based on the results, authors recommend following interventions for ‘jumper’s knee’ treatment: weight loss, improving upper-leg flexibility and quadriceps strength, addressing dysfunctions in the muscle/tendon complex and in the pelvic and lower limb kinetic chain and use of orthotics.
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